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Abstract
Purpose: Measurement of contrast sensitivity (CS) across the visual field (VF) is critical in assessing the integrity of the visual system. Questions that remain to be addressed in the use of conventional clinical perimetry techniques include: How does CS change with age across the VF? Are static and kinetic perimetry results actually the same? Can factors causing increased measurement variability in perimetry be systematically quantified and eliminated? Thus, the aim of this thesis is to address these specific limitations of clinical perimetry that may introduce measurement variability, with the overall hypothesis that through optimising the psychophysical task, contrast sensitivity can be determined more accurately.
Methods: Subjects with normal ocular health and patients with glaucoma were recruited to undertake psychophysical testing using a variety of instruments. Normal subjects were used to generate normative data which would then form the basis for comparison for glaucoma patients. VF and CS testing was performed using clinical- and laboratory-based techniques.
Results: Inter-individual variability of measurements for a VF normative database can be minimised using an appropriate sample size. Both age-related and age-corrected contrast sensitivity isocontours (CSIs) across the VF were identified. In doing so, we developed a large normative database for sensitivities measured using Goldmann test sizes I-V. This was subsequently used to optimise the stimulus test size to detect early glaucomatous field defects. A model predicting the lead-time gained using an optimised stimulus size was determined and tested. Reducing conditions of high uncertainty using attentional cueing showed improved CS. Finally, we reconciled the differences between static perimetry sensitivities, as identified by the CSIs, and kinetic perimetry isopters. A more robust psychophysical procedure that eliminates biases attributable to the clinical procedures eliminates the dissociation between static and kinetic perimetry techniques.
Conclusions: Fidelity of CS measurements within the VF can be improved by: 1) understanding the age-related changes in vision, 2) reconciling the differences between measurement techniques and 3) reducing the contribution of sources of measurement variability. Modifications to
conventional perimetric test paradigms can easily translate to improved detection rates of ocular diseases and accurate assessment of the ageing visual system.